FIG. 5 shows the schematic structure of a conventional exposure apparatus. Reference numeral 31 denotes a light source of the exposure apparatus used in the semiconductor manufacture, and the like. For further miniaturization of exposure patterns, the light source 31 tends to use light having a shorter wavelength. The light source 31 has advanced from an i-line source to an excimer laser. The laser light source has further advanced from a KrF excimer laser to an ArF excimer laser. At present, in order to satisfy a demand for further micropatterning, it is proposed to use an F2 laser or an EUV light source.
Light emitted from the light source 31 is guided to an illumination optical system 33 through an introduction port 32. The illumination optical system 33 removes an illumination variation and shapes the beam. Then, the resultant beam is applied, as illumination light, to a reticle 34 as an original of an exposure pattern. The reticle 34 is placed on a reticle stage 35.
The light transmitted through the reticle 34 serves as pattern light to reduce and to project a pattern onto a wafer 37 arranged in a plane optically conjugate to that of the reticle 34 through a projection optical system 36.
The wafer 37 is placed on a wafer stage 38 driven by a linear motor, and undergoes step and repeat overlay exposure. Along with the necessity of a smaller integrated circuit line width, there has been developed the following semiconductor exposure apparatus. That is, the apparatus narrows down an exposure area to a slit at the central portion of the projection optical system 36, at which optimal imaging is possible. Then, the apparatus also drives the reticle stage 35 by a linear motor to expose the wafer while synchronously scanning the wafer stage 38 and reticle stage 35.
In recent years, a liquid immersion exposure apparatus has received a great deal of attention, which executes exposure while filling, with a liquid such as pure water, an exposure light transmission space (also to be referred to as a liquid immersion portion or a liquid immersion region hereinafter) between the wafer 37 and the lowermost surface of the projection optical system 36. By adopting such liquid immersion, a high numerical aperture (NA) can be attained owing to a high refractive index of a liquid. This amounts to grasping a chance to easily realize further micropatterning by adding a liquid immersion apparatus to an existing ArF exposure apparatus as a base without any F2 laser or EUV light source, which applies a large installation load (see, e.g., Japanese Patent Laid Open No. 6-124873).
FIG. 6 is a view showing an example of the form of a liquid immersion exposure apparatus. FIG. 6 shows an arrangement in the case of local liquid immersion. In liquid immersion exposure, a liquid immersion region is formed to be partitioned by a liquid immersion wall 21 on the lowermost surface of the projection optical system 36. A liquid supply nozzle 22 and liquid recovery nozzle 23 are arranged to face the liquid immersion region. Liquid immersion exposure is based on the following method. That is, the liquid supply nozzle 22 supplies a predetermined amount of a liquid immersion fluid in synchronism with recovery by the liquid recovery nozzle 23. With this operation, exposure is executed in the liquid immersed state, in which the liquid immersion region is filled with a liquid immersion fluid.
Since a liquid used for liquid immersion (also to be referred to as a liquid immersion fluid hereinafter) is regarded as even part of an optical device, it is demanded to strictly control purity, flow rate, and temperature. Ultra pure water is generally used as the liquid immersion fluid. Ultra pure water produced from factory equipment is thermoregulated by a cooler 24, heater 25, temperature sensor 26, and thermoregulator 27 through a supply line 28 with a supply valve 30, and supplied to a liquid immersion region through the liquid supply nozzle 22.
When ultra pure water is to be used as the liquid immersion fluid, in order to avoid mixing of impurities, such as particles or ions, the material of a liquid contact portion is limited to Teflon® based and glass based materials, and resins such as vinyl chloride, and metal based materials cannot be used. This naturally applies to the materials of the cooler 24, heater 25, and temperature sensor 26 having liquid contact portions, which contact the liquid immersion fluid.
Unfortunately, when a material such as Teflon (trademark) is used for a device which thermoregulates the liquid immersion fluid, its heat transfer characteristic worsens. In particular, assume that ultra pure water is provided from factory equipment under the condition in which its flow rate and temperature are largely varied. In this case, the liquid immersion fluid is supplied to a liquid immersion region while disturbances are not completely eliminated, due to a bad response characteristic of the thermoregulation system. Accordingly, there is a possibility that the imaging performance of liquid immersion exposure is decisively damaged.
Moreover, since a follow up characteristic with respect to a heat capacity variation at the start of the supply degrades, the operator must wait until the temperature stabilizes, resulting in a decrease in throughput.